Conventional mechanical seal assemblies are employed in a wide variety of environments and settings, such as for example, in mechanical apparatuses, to provide a fluid-tight seal. The sealing assemblies are usually positioned about a rotating shaft or rod that is mounted in and protrudes from a stationary mechanical housing.
Split mechanical seals are employed in a wide variety of mechanical apparatuses to provide a pressure-tight and fluid-tight seal. The mechanical seal is usually positioned about a rotating shaft that is mounted in and protruding from a stationary housing. The mechanical seal assembly is usually bolted to the outside of the housing at the shaft exit, thus preventing the loss of pressurized process fluid from the housing. Conventional split mechanical seals include face-type mechanical seals, which include a pair of sealing rings that are concentrically disposed about the shaft and are axially spaced from each other. The sealing rings each have sealing faces that are biased into sealing contact with each other by conventional biasing mechanisms, including biasing clips or springs. Usually, one seal ring remains stationary (i.e., the stationary seal ring) while the other ring contacts the shaft and rotates therewith (i.e., the rotary seal ring). The mechanical seal prevents leakage of the pressurized process fluid to the external environment by biasing the seal ring sealing faces in sealing contact with each other. The rotary seal ring is usually mounted in a holder assembly which is disposed in a chamber formed by a gland assembly. The holder assembly may have a pair of holder halves secured together by a screw. Likewise, the gland assembly may have a pair of gland halves also secured together by a screw. The sealing rings are often split into segments, where each segment has a pair of sealing faces, thereby resulting in each ring being a split ring that can be mounted about the shaft without the necessity of freeing one end of the shaft ends.
Conventional seal rings are initially formed as a unitary single seal element in the shape of an annulus. A pair of grooves is formed along the inner diameter portion at opposite positions and extends in the axial direction from the top to the bottom of the seal ring. These grooves are formed in the seal element using well known techniques, including the use of conventional reciprocating machines or grinding disks. Once the grooves are formed, a pressure is applied on the inside of the seal ring at a location approximately ninety degrees from the grooves in the radially outward direction sufficient to fracture and split the seal ring element along the grooves. The resultant seal ring segments have axial exposed faces that are relatively flat and smooth. Any surface irregularities are nominal and are typically solely the result of the grain structure of the seal ring material.
Prior split mechanical seals have rotary and stationary components assembled around the shaft and then bolted on to the equipment to be sealed. A rotary seal face is inserted into a rotary metal clamp after the segments are assembled around the shaft. Then, the stationary face segments and gland segments are assembled and the split gland assembly is then bolted to the pump housing.
Previous split mechanical seal designs posed several problems. A first problem with prior split mechanical seal designs relates to the insertion of the rotary seal ring into the holder assembly that is clamped around the shaft. An O-ring seals the rotary seal face to the clamped holder in an axial direction. The rotary seal face must be pushed into a tight space inside the clamped holder, and some difficulty may often be encountered. The elastomeric O-ring sealing the rotary seal face to the holder needs to be compressed for sealing, and a certain amount of force is required to insert the seal face inside the clamped holder. In addition, since the O-ring tends to grab the seal ring and inhibits sliding, the rotary seal face of prior art mechanical seal assembly designs has a tendency to “pop-out” after being inserted. Further, the movement of the O-ring when installed can result in the O-ring being disposed in an angled position, rather than a more preferred seated position relative to the rotary seal ring. From the angled position, the installer would be required to move the O-ring back to the original position, which is quite difficult to do. This process can require multiple attempts during installation to have the rotary seal face properly seated inside the clamped holder.
Another important consideration is to maintain the perpendicularity of the rotary seal face to the shaft for smooth operation. It is quite possible to have one side or split segment of the rotary seal face further inside the clamped holder than the other side. The result is an out-of-squareness condition of the rotary seal face with respect to the shaft axis. This in turn creates a back and forth motion of the stationary seal ring as it tilts from side to side in order to track the rotary seal ring with every shaft revolution. If significant enough, this can result in shortened seal life.
A further problem exists when the installer is assembling the mechanical seal around the shaft at the installation site. It is quite difficult for the installer to keep the rotary seal ring halves aligned relative to each other. Similarly, it is also difficult for the installer to keep the stationary seal ring halves aligned. As the seal rings are brought in to contact with each other, the seal ring halves float relative to each other because of their split nature. The installer must therefore constantly align the halves in order to ensure proper installation. As the remainder of the mechanical seal assembly is placed about the seal rings, the biasing mechanisms prematurely force the seal rings into contact with each other. The installer therefore must manually overcome this biasing force during installation. The consequence of these various issues is that the seal rings are constantly coming into forceful contact with each other, which often results in damage to the seal rings.
Moreover, since the axial split surfaces of the seal ring halves are relatively smooth and flat, it is also difficult for the installer to keep the faces aligned during installation.